Method for adjusting a coolant flow by means of a heating cut-off valve

ABSTRACT

The invention relates to a method for actuating the valves in the three-way thermostat and in the heating cut-off valve of a cooling system. The valve setting in the cooling system is in this case selected such that during the warm-up phase of the engine, until the latter has reached its operating temperature, the coolant in the cooling ducts is brought to rest until the coolant temperature exceeds a predefined reference value.

CROSS REFERENCE TO RELATED APPLICATION

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/EP2004/008616, filed Jul. 31, 2004,and claims priority of German Patent Application 103 37 413.2, filedAug. 14, 2003.

BACKGROUND OF THE INVENTION

The invention relates to the adjustment of the coolant flow by means ofa heating cut-off valve, in particular for a cooling system in a motorvehicle. During the warm-up phase of the internal combustion engine, theheating cut-off valve acting together with a three-way thermostatensures that coolant is stationary in the coolant ducts of the engineblock so that the warm-up phase of the internal combustion engine takesas short a time as possible.

The invention proceeds from a prior art as is for example known from theGerman patent application DE 100 12 197 A1. In this cooling system foran internal combustion engine, too, a cut-off valve in the coolant linebetween an engine block and a heating heat exchanger, and a three-wayvalve for switching between a large and a small coolant circuit, acttogether in order to shorten the warm-up phase of the internalcombustion engine to as great a degree as possible.

For this purpose, however, the waste heat from a climate control unit isutilized in order to heat the coolant with the waste heat from theheating heat exchanger of the climate control unit when the engine isstill cold.

The coolant heating from DE 100 12 197 A1 has the disadvantage that itis only effective in conjunction with a climate control unit, even thisonly being the case if the ambient conditions are such that a climatecontrol unit generates an appreciable quantity of waste heat as a resultof cooling activity. This is generally the case when starting a motorvehicle in summer if the vehicle has been standing in the sun. At warmambient temperatures, however, the warm-up phase of an internalcombustion engine is not very long, so that in summer, compliance withemissions limits is not a problem. These problems occur more intenselyat cold ambient temperatures as are encountered in winter in thenorthern hemisphere. However, the climate control unit then produces nowaste heat, so that the abovementioned heating of the coolant is notavailable when it is needed most.

DE 44 32 292 A1 discloses a cooling system for an internal combustionengine in a motor vehicle, in which the coolant flow through a heatingheat exchanger is adjusted in order to assist the internal combustionengine in warming up. However, a very complex distributor device havinga total of 6 valves is proposed for this purpose. The complexdistributor device is necessary since the coolant pump is drivenpermanently and thus the coolant flow through the heating heat exchangeris required as a bypass for the disconnected coolant cooler. Three-waythermostats or three-way valves are not used. DE 44 32 292 A1 does nottherefore form a generic prior art for the invention claimed here.

A number of approaches are known from the previously known prior art forshortening the warm-up phase of an internal combustion engine to asgreat a degree as possible. Previously, however, a permanent coolantflow has always been maintained in the engine block, even during thewarm-up phase of the internal combustion engine. For this purpose,valves were used to adjust the coolant flow through the heating heatexchangers.

It is therefore an object according to the invention to further improvethe control of the coolant flow through the heating heat exchangers, inorder to be able to further shorten the warm-up phase of an internalcombustion engine.

SUMMARY OF THE INVENTION

The above object generally is achieved according to the presentinvention by a method for adjusting the coolant flow from the coolingducts of an internal combustion engine into a heating heat exchangerwith a cut-off valve, wherein the coolant flow into the heating heatexchanger is interrupted by the cut-off valve if the temperature of thecoolant is below a predefined reference temperature, and the coolantflow in the combustion ducts is thus stopped. Further advantageousembodiments are described in and description of the exemplaryembodiments.

The solution is successful primarily by means of suitable actuation ofthe valves in the three-way thermostat and in the heating cut-off valve.The valve setting in the cooling system is in this case selected suchthat during the warm-up phase of the engine, until the latter hasreached its operating temperature, the coolant in the cooling ducts isbrought to rest until the coolant temperature exceeds a predefinedreference value.

In one advantageous embodiment of the invention, the heating cut-offvalve can, if the coolant temperature has exceeded a preliminarythreshold, be opened for a short time in order to allow pre-warmedcoolant to flow around the wax pellet in the three-way thermostat.

Thereafter, the coolant is prevented from flowing in the cooling ductsof the internal combustion engine again until the operating threshold isreached. The temporary opening prepares the three-way thermostat for theimminent start of operation as a thermostat for controlling the coolanttemperature.

In another advantageous embodiment of the invention, overload protectionis realized for preventing local overheating in the internal combustionengine during the warm-up phase. For this purpose, an expected coolanttarget temperature is calculated as a function of the engine parameters,in particular as a function of the load torque which is present and thecurrent engine speed. If whilst the coolant is stationary in theinternal combustion engine, that is to say if the coolant ducts areclosed off, the actual coolant target temperature is below the expectedtarget temperature in spite of the presence of a high load, this is anindication of boundary layer formation in the cooling ducts whichprevents heat transfer when the coolant is stationary. There is then adanger of the internal combustion engine overheating. In this case, thecoolant flow is started up in the cooling ducts even if the coolanttemperature has not yet reached the opening temperature for the cut-offvalves. As an alternative to opening the heating cut-off valve, the waxpellet in the three-way thermostat can also be subjected to flow inorder to provide protection from overheating.

Exemplary embodiments of the invention are described in more detail inthe following on the basis of the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of a cooling system having the mostimportant influential parameters for actuating the heating cut-offvalve,

FIG. 2 shows a preliminary controller for pre-heating a three-waythermostat in the cooling circuit,

FIG. 3 shows a method for overload protection whilst the coolant isstationary in the cooling ducts of the internal combustion engine,

FIG. 4 shows a block diagram of the principle of integrating theinvention in a motor vehicle having climate control.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 schematically shows a typical cooling system for a six-cylinderinternal combustion engine 1. In addition to the internal combustionengine, a vehicle cooler 2 and a heating heat exchanger 3 are integratedin the cooling system. The cooling power of the vehicle cooler can beinfluenced by means of an electrically driven fan 4. In order to adjustthe fan power, the electric motor of the fan is controlled by a controlunit 5. Cooled coolant is taken from the vehicle cooler by means of theadvance line 6 and is fed by means of the coolant pump 7 into thecooling lines 8 in order to be fed to the cooling ducts (not illustratedin more detail) for the combustion cylinders 9. The heated coolant isled from the combustion cylinders 9 to a three-way thermostat 11 bymeans of return lines 10. Depending on the setting of the valves in thethree-way thermostat 11, the coolant travels out of the internalcombustion engine back into the vehicle cooler via the cooler return 12or back into the cooling lines 8 of the internal combustion engine viathe cooler short circuit 13 and the coolant pump 7.

Depending on the setting of the valves in the three-way thermostat 11,the cooling system can in this case and in a manner known per se beoperated in a short circuit operating mode, in a mixed operating mode orwith the large cooling circuit. The heating heat exchanger 3 isconnected by means of a temperature-controlled cut-off valve 14 to thehigh-temperature branch of the cooling system in the internal combustionengine. The flow rate through the heating heat exchanger after thecut-off valve 14 is opened can, in order to adjust the heating power, beadjusted by means of an additional electric coolant pump 15 and asynchronized cut-off valve 16.

The actuation of the actuating elements on the valves of the three-waythermostat 11 is set in this case by the control unit 5. A logiccomponent Logic in the form of a microelectronic processor is containedin the control unit. The control unit is preferably formed by thecontrol unit of the engine electronics. In the logic component, thecontrol algorithms sketched in FIGS. 2 and 3 are implemented in the formof software programs. The most important operating data for theadaptation of the control parameters are in this case the cooling watertemperature, the coolant target temperature, a failure recognitionsignal Failsafe, the current torque which is present at the internalcombustion engine and also various reference values Ref2Min, Ref2Max,Ref3, Ref1 a and Ref1 bn which are significant for the decisionprocesses as discussed in conjunction with FIGS. 2 and 3. Finally, thecut-off valve 14 is opened or closed by means of the control unit 5 as afunction of the decision routines in the control unit. To enable theinternal combustion engine to reach its operating temperature as quicklyas possible, the coolant flow in the cooling ducts of the internalcombustion engine can, with suitable valve setting in the three-waythermostat 11, be brought to rest by means of the heating cut-off valve14 until a threshold temperature is reached at which the coolant flow isthen started up and the internal combustion engine is thus cooled. Theinterruption according to the invention of the cooling during thewarm-up phase of the internal combustion engine results in the latterreaching its operating temperature more quickly.

In this case, the heating cut-off valve 14 initially remains closeduntil the cooling water temperature exceeds at least one temperaturethreshold value. The corresponding decision algorithm is graphicallyillustrated in a simplified manner in FIG. 2. The decision algorithm isimplemented as a software program in the control unit 5. The coolingwater temperature which is determined by means of a sensor S is comparedwith a predefined and stored reference value Ref1 a by means of amagnitude comparison 20 which is preferably realized in terms ofprogramming. Said reference value is in this case an engine-specifictemperature reference value which indicates the operating threshold foractivating the coolant flow. If the current cooling water temperatureexceeds this engine-specific operating threshold, a subsequent logic inthe control unit 5 sends the corresponding control signal for openingthe heating cut-off valve to its actuators, and the heating cut-offvalve is opened for operating the vehicle heating.

The operating threshold can advantageously be assigned a second, lowertemperature threshold Ref1 b as a preliminary threshold and be connectedin parallel in terms of programming. If the cooling water temperatureexceeds the preliminary threshold, the heating cut-off valve can betemporarily opened in order to effect a flow of previously heatedcooling water via the wax pellet in the three-way thermostat 11. As aresult, the three-way thermostat is prepared for the imminent start ofoperation of the cooling system. Expediently, the cooling watertemperature is exceeded by means of a programmed comparison step 21 andthe heating cut-off valve is temporarily opened by means of a programmedtime controller 22. The two program loops for monitoring the operatingthreshold and for monitoring the preliminary threshold can alternativelybe supplied by means of an OR-gate 23 to the subsequent processcontroller.

Stationary cooling water in the cooling ducts of the internal combustionengine holds the danger of local overheating in the internal combustionengine as a result of boundary layer formations which, when the coolingwater is stationary, can form largely unnoticed by the temperaturesensor. It is therefore advantageous to make safety provisions, by meansof which local overheating can be prevented in good time. Onepossibility for this is shown by the exemplary embodiment of FIG. 3.

A temperature sensor S and two comparison steps 30, 31 monitor whetherthe cooling water temperature is in a range between an upper referencevalue Ref2Max and a lower reference value Ref2Min. The expectedload-dependent cooling water target temperature TM_ECT is calculated bymeans of an engine model from the current torque or preferably thecurrent torque profile. This cooling water target temperature iscompared as overload protection to a further reference value Ref3 bymeans of a further comparison step 32. If the cooling water temperaturecalculated from the engine load is above a limit value for overloadprotection, or if the calculated cooling water temperature is above thecurrent cooling water temperature and if at the same time the coolingwater temperature is in a temperature range below the operatingthreshold of the cooling system, the coolant flow is started up as aprecautionary measure in order to prevent local overheating for reasonsof safety. The coolant flow is effected by alternatively opening theheating cut-off valve 14 or by a suitable valve setting in the three-waythermostat 11. The exemplary embodiment in FIG. 3 favors thesimultaneous existence of two conditions for starting up the earlycoolant flow, namely that the cooling water temperature must be in acertain temperature interval between a lower reference value Ref2Min andan upper reference value Ref2Max and that the load-dependent calculatedcooling water target temperature must be above a comparison value. Interms of programming, these two conditions are combined by means of anAND-gate 33. This approach has the advantage that if the cooling watertemperature is not in the predefined temperature interval, thecalculation of a load-dependent cooling water target temperature remainsunconsidered and can be omitted. If the engine has reached its operatingtemperature, the overload protection and thus the calculation of aload-dependent cooling water target temperature can therefore beswitched off by retrieving the temperature interval. This relieves theprocessing capacity in the control unit 5 of load.

In a more simple embodiment, overload protection can also be obtained bymeans of simple comparison of the calculated, load-dependent coolingwater target temperature TM_ECT with a comparison temperature, eitherthe actual cooling water temperature or with a reference value Ref3. Thecoolant flow is then effected by opening the corresponding valves everytime the calculated cooling water target temperature is above thecomparison value.

Finally, if a failure recognition signal Failsafe is present for reasonsof safety, the coolant flow can be started up for reasons of safety byopening the heating cut-off valve and by actuating the correspondingvalves in the three-way thermostat. A failure recognition signal can forexample be generated by self-testing of the control unit or betransmitted by signal lines if other components are operatingdefectively.

FIG. 4 shows a block diagram for integrating the decision processes fromFIG. 2 and FIG. 3 in a motor vehicle having a climate control system 41.Experience has shown that the motor vehicle driver's customer wishesmust be incorporated. That is to say, it must be possible for the driverto influence the decision processes as they are illustrated in FIG. 2and FIG. 3. This is in particular the case when the motor vehicle driverwishes to start up the heating because he is too cold. In this case,after suitable actuation of the heating controller, a signal for aheating demand is sent from the climate control system 41 to the logicof the control unit 5. A superordinate prioritizer 43, which is likewiserealized as a software module in the control unit 5, then prioritizesthe various demands for actuating the heating cut-off valve, which canbe simultaneously present from the heating demand of the climate controlsystem, the actuation of the cut-off valve according to FIG. 2 or theactuation of the cut-off valve according to FIG. 3. In this case, theprioritization allows a certain precedence to be assigned to the heatingdemand in particular. This precedence is allowed for example by means ofa time controller in such a way that after a heating demand has beenpresent for a minimum duration of for example 2 minutes, the heatingdemand is allowed absolute priority and the heating cut-off valve isopened in any case irrespective of other operating parameters. Ifdesired, the heating demand from the climate control unit can also ofcourse always and in any case be allowed priority as soon as the heatingdemand is made. In this last-mentioned alternative, however, the virtuesof the decision methods according to FIG. 2 and FIG. 3 would be at leastpartially negated.

1. A method for adjusting the coolant flow from the cooling ducts of aninternal combustion engine into a heating heat exchanger with a cut-offvalve, with the cooling ducts are additionally connected to an enginecooler via a three-way thermostat, including the steps of interruptingthe coolant flow into the heating heat exchanger by the cut-off valve ifthe temperature of the coolant is below a predefined referencetemperature (Ref21 a, Ref1 b, Ref2Min), and the coolant flow in thecombustion ducts is thus stopped; after a first reference temperature(Ref1 b) as a preliminary threshold is exceeded, temporarily opening thecut-off valve, so that a wax pellet in the three-way thermostat ispre-heated; and the cut-off valve is subsequently closed again until thecoolant temperature has reached a second, higher reference value (Ref1a) as an operating threshold.
 2. The method as claimed in claim 1,wherein if the temperature of the coolant in a lower temperature rangebetween a lower reference temperature (Ref2Min) and an upper referencetemperature (Ref2Max) and a load-dependent, calculated cooling watertarget temperature simultaneously falls below a third reference value(Ref3), the coolant flow in the cooling ducts of the internal combustionengine is started up by correspondingly opening the cut-off valve or arelated valve in the three-way thermostat.
 3. The method as claimed inclaim 1, wherein the coolant flow is started up by correspondinglyopening the cut-off valve or a related valve in the three-way thermostatif the calculated, load-dependent coolant target temperature exceeds acomparison value.
 4. A method for adjusting the coolant flow from thecooling ducts of an internal combustion engine into a heating heatexchanger with a cut-off valve, with the cooling ducts are additionallyconnected to an engine cooler via a three-way thermostat, including thesteps of interrupting the coolant flow into the heating heat exchangerby the cut-off valve if the temperature of the coolant is below apredefined reference temperature (Ref21 a, Ref1 b, Ref2Min), and thecoolant flow in the combustion ducts is thus stopped; and, if thetemperature of the coolant in a lower temperature range between a lowerreference temperature (Ref2Min) and an upper reference temperature(Ref2Max) and a load-dependent, calculated cooling water targettemperature simultaneously falls below a third reference value (Ref3),the coolant flow in the cooling ducts of the internal combustion engineis started up by correspondingly opening the cut-off valve or a relatedvalve in the three-way thermostat.
 5. A method for adjusting the coolantflow from the cooling ducts of an internal combustion engine into aheating heat exchanger with a cut-off valve, including the steps ofinterrupting the coolant flow into the heating heat exchanger by thecut-off valve if the temperature of the coolant is below a predefinedreference temperature, and the coolant flow in the combustion ducts isthus stopped; and, the coolant flow is started up by correspondinglyopening the cut-off valve if the calculated, load-dependent coolanttarget temperature exceeds a comparison value.